Abstract:

Appropriate nutrient addition can improve grassland productivity and stability， but the effects of adding different amounts of nutrients on large-scale grassland communities are unclear. In this study， fertilization experiments were carried out in a field experiment on mildly degraded natural mowed grassland in Hulunbuir with a total area of 182673 m². Urea granules， calcium superphosphate granules， and potassium sulfate granules were used to supply nitrogen （N）， phosphorus （P）， and potassium （K）， respectively. Three nutrient addition treatments （A， B， C） and a control （CK） were established. The application rates of N， P₂O₅， and K₂O were 2.3， 1.2， and 0.75 g·m^-2， respectively， in treatment A； 4.6， 2.4， and 1.5 g·m^-2， respectively， in treatment B； and 6.9， 3.6， and 2.3 g·m^-2， respectively， in treatment C. No fertilizer was applied to the CK. The fertilizers were applied twice， once in mid-July and once in early August 2022 in the middle of the growing season. We compared the effects of these fertilization treatments on the characteristics of grassland communities. The results showed no synergistic effect of the treatments on the productivity and species diversity of the grassland. Treatment A did not significantly affect the community biomass， but significantly increased the community richness index. The community biomass was 201.73 g·m^-2 in CK， and was higher in treatment B （319.19 g·m^-2） and treatment C （328.52 g·m^-2）， although the community species diversity did not differ significantly between CK and treatments B and C. Treatments B and C significantly increased the biomass of dominant species and perennial bunch grasses. Treatment B significantly increased the biomass of perennial forbs. The increase in community biomass in treatments B and C was associated with increases in community species height and density. Treatments A， B， and C significantly enhanced the carbon， N， and P contents in the community. The contents of carbon， N， and P in the communities in treatments A， B， and C were all significantly and positively correlated with community biomass. In conclusion， fertilization mitigates the effects of nutrient-limiting factors on plant growth and enhances community biomass by increasing the biomass of key species in the community.

Key words: Hulunbuir grassland, biodiversity, grassland productivity, stoichiometric ratio, plant functional group, community members